Cellular communications have become widespread in recent years. As spread-spectrum code division multiple access (CDMA) systems become more prevalent in today's cellular systems, a need has arisen to provide test equipment for the CDMA cellular base station telephone equipment.
The testing of CDMA base station telephone equipment is specified in the Telecommunication Industry Association (TIA) Interim Standard 97 (IS-97). Among the tests specified by IS-97 are a class of parameters designed to measure what is hereinafter referred to as the CDMA base station "waveform quality." These waveform quality parameters provide a characterization of the code domain channels of a CDMA base station transmitter. One measurement, code domain power, is used to measure the distribution of power among code channels. Other measurements such as code domain timing and code domain phase, reflect timing and phase errors of code channels relative to the pilot channel. These measurements are important because subscriber units make all measurements of code channels based on timing and phase of the received pilot channel. IS-97 provides for maximum offsets in phase and timing to guarantee that subscriber units will function satisfactorily.
Within IS-97, it is suggested that the waveform quality parameters be measured using certain computationally complex algorithms. Specifically, IS-97 suggests that a large number of simultaneous equations be solved continuously during the measurement process. The continuous solving of a large number of simultaneous equations is costly in terms processing power and time. It is desirable, therefore, to reduce or eliminate the need for simultaneous equation solving, thereby reducing the hardware and time required to perform the measurements.
Further, it is recognized in the art that measurement accuracy can be substantially increased by increasing the length of a correlation in the suggested algorithm as presented in IS-97. It is also well recognized in the art that as the correlation length is increased, the frequency offset of the input signal must be controlled more tightly to minimize the phase rotation during any one correlation time. It is desirable, therefore, to be able to increase measurement accuracy by increasing the correlation time without necessitating tighter input frequency control.
Hence, there exists a need for an apparatus and method for measuring CDMA base station waveform quality parameters which is both computationally simpler and faster than current approaches as known in the art.